1. Field of the Invention
This invention relates to a thread fastening type connector assembly comprising two connectors which are fastened to each other utilizing a bolt and nut arrangement.
2. Background
A conventional thread fastening type connector assembly is disclosed in Japanese Patent Application (OPI) No. 188188/1987 (the term "OPI" as used herein means an "unexamined published application"), and illustrated in FIGS. 8 and 9. The connector comprises a male connector 32 and a female connector 33 engageable with the male connector. The male connector 32 has a center portion 34 in which a nut 35 is fixed, and a plurality of terminal accommodating chambers 52 in which female terminals 36 are disposed. The female connector 33 includes a bolt 37 extending along the longitudinal axis of the connector and aligned with the nut 35 in the male connector 32, and a plurality of terminal accommodating chambers 38 in which male terminals 39 are disposed. In order to facilitate the threaded engagement of the bolt 37 with the nut 35, the shank 40 of the bolt 37 extends through a bolt holder 41 made of synthetic resin. As shown in FIG. 9, the bolt holder 41 is disposed within a central opening 43 formed in the housing 42 of the female connector 33, and is engaged therewith by means of protrusions 44 and 44 engaged in locking grooves 45 and 45 formed in the housing 42.
In the thread fastening type connector assembly, a connector engagement detecting rod 46 is axially disposed within a bore provided in the bolt holder 41. When the male connector 32 and the female connector 33 are engaged with each other, the detecting rod 46 is urged upwardly by the center portion 34 of the male connector 32 so as to protrude from a through-hole 47 thereby indicating to the operator that complete engagement of the connectors has been accomplished. Therefore, the operator will not excessively tighten the connectors to each other.
As another means for preventing excessive tightening of the connectors to each other, a breaking recess 48 is formed in the shank 40 of the bolt 37 so that the shank will shear if too much torsional force is applied. To retain the bolt in a predetermined axial position, a locking ring 50 is secured to the bolt 37 between the shank 40 and the threaded portion 49, as illustrated. A washer 52 is mounted on the bolt 37 just below the head 51. Thus, as the bolt 37 is tightened, the force of the head 51 is applied through the washer 52 against the bolt holder 41, so that the female connector 33 is engaged with the male connector 32.
In the conventional thread fastening type connector assembly thus designed, the tightening force of the bolt 37 is directly applied to the bolt holder 41 and, therefore, it is necessary to use an expensive material such as a glass-fiber reinforced PBT (polybutyleneterephthalate) resin to form the bolt holder 41; that is, the bolt holder 41 must be high both in mechanical strength and rigidity. Thus, the conventional thread fastening type connector assembly is relatively high in manufacturing cost.